1. Field of the Invention
The present invention relates to an optical data or information recording-reproducing method and an apparatus using the method. More particularly, the present invention relates to an optical information recording-reproducing method and an apparatus using the method in which a light spot is moved relative to a track of an optical information recording medium, while auto-tracking (AT) and auto-focusing (AF) of the spot relative to the recording medium are performed in order to record information on the medium and to reproduce and/or erase information recorded in the medium.
2. Related Background Art
Conventionally, various kinds of media, such as a disc card, tape or other types, have been known as optical information recording media. Information or recorded information in or from an optical information recording medium is recorded or reproduced using a light beam. Among them, card-shaped optical information recording media (hereinafter referred to as an optical card) are expected to be in a great demand because the information recording medium is small in size, light in weight, easy to carry and has a large recording capacity. FIG. 2 is a schematic plan view illustrating the structure of an optical card.
In FIG. 2, an optical card 101 is provided with an information or data recording area 102 at both opposite ends of which track selection areas 104a and 104b are formed. A plurality of information tracks 103 are arranged in a portion of the data recording area 102 and the track selection areas 104a and 104b. Information or data is recorded on the data tracks 103. Reference numeral 105 designates a home position of a light spot.
The optical card 101 is scanned with a light beam that is modulated based on recording data and condensed into a minute spot, and data or information is recorded in the optical card 101 as an array of optically detectable record pits or a data track.
At this time, in order to accurately record data without any trouble, such as the intercrossing of data tracks, it is necessary to control the irradiation position of the light spot on the optical card 101 in a direction orthogonal to a scanning direction. This control is termed auto-tracking and will hereinafter be referred to as AT. Further, in order to apply a light beam as a stable minute spot irrespective of warps of the optical card 101 and mechanical errors, it is necessary to control the light spot in a direction perpendicular to the surface of the optical card 101. This control is termed auto-focusing, and will be referred to as AF hereinbelow. Those AT and AF are also needed at the time of data reproduction.
FIG. 1 shows an example of an optical information recording-reproducing apparatus.
In FIG. 1, reference numeral 106 designates a motor for moving the optical card 101 in the directions indicated by arrows. Reference numeral 107 designates a light source such as a semiconductor laser. Reference numeral 108 designates a collimator lens for collimating a light beam from the light source 107. Reference numeral 109 designates a beam splitter, and reference numeral 110 designates an objective lens. Reference numeral 111 designates a coil for tracking control. Reference numeral 112 designates a coil for focusing control. Reference numerals 113 and 114 respectively designate condenser lenses. Reference numerals 115 and 116 respectively designate photoelectric conversion elements. Reference numeral 117 designates a tracking control circuit, and reference numeral 118 designates a focusing control circuit. In response to instructions or commands from the control circuits 117 and 118, currents are caused to flow in the tracking coil 111 and in the focusing coil 112 respectively. These instructions or commands are based on tracking and focusing signals detected by the photoelectric conversion elements 115 and 116, and cause the objective lens 110 to be properly moved. Thus, AT and AF are accomplished.
Further, reference numeral 119 designates a system controller for controlling the information recording-reproducing apparatus, and reference numeral 120 designates a group of various control signals output from the controller 119. Although signals other than the control signal group 120 as shown in FIG. 1 are output from the controller 119, they are not illustrated in FIG. 1. There are further shown an optical head 121 and a driving motor 122 for moving the optical head 121 in a direction u as indicated in FIG. 2.
A light beam from the light source 107 is collimated by the collimator lens 108, and after passing the beam splitter 109, the collimated beam is condensed onto the recording track of the optical card I01 by the objective lens 110. Light reflected by the recording track is in turn passed through the beam splitters 109 and split into two beams. These beams are respectively condensed onto the photoelectric conversion element 115, for detecting a tracking signal, and the photoelectric conversion element 116, for detecting a focusing signal, by the condenser lenses 113 and 114. The signals obtained by the respective photoelectric conversion elements 115 and 116 function as a tracking error signal and a focusing error signal in the tracking and focusing control circuits 117 and 118 to cause currents to flow into the tracking and focusing coils 111 and 112. Thus, the objective lens 110 is moved to achieve AT and AF.
FIG. 3 is a schematic view showing the structure of the focusing control circuit 118 shown in FIG. 1.
In FIG. 3, reference numeral 201 designates an amplifier for amplifying an electric focusing signal from the photoelectric conversion element 116 to a proper voltage. Reference numeral 203 designates an analog switch. An output of the amplifier 201 is input into one input terminal of the analog switch 203 while an output of an adder or summing circuit 208 is input into the other input terminal of the analog switch 203 through a point C. A signal from a focusing controller 205 selects one of the input terminals of the analog switch 203. Reference numeral 206 designates a circuit for generating a triangle wave and is referred to as a TW circuit. Reference numeral 207 designates a circuit for generating a square wave and is referred to as an SW circuit. The outputs of the SW and TW circuits are added up in the adder circuit 208. Reference numeral 204 designates a driver, and the driver 204 causes a driving signal current to flow into the focusing coil 112, in response to a signal from the analog switch 203. Reference numeral 205 designates a focusing controller for controlling the entire focusing control circuit 118 in response to the signal 120 from the system controller 119. Although the signal of the focusing controller 205 is input solely into the analog switch 203 as shown in FIG. 3, signals other than those shown in FIG. 3 are output from the focusing controller 205. These other signals from the focusing controller 205 are not shown in FIG. 3.
FIGS. 4A and 4B are respectively graphs illustrating changes in voltages at points C and A of the focusing control circuit 118 shown in FIG. 3.
The draw-in or closure of a focusing servo will be described with reference to FIGS. 3, 4A and 4B.
Initially, as shown in FIG. 3, the A point side of the analog switch 203 is brought into an open state and the C point side thereof is brought into a closed state, in response to the signal D from the focusing controller 205. Hence, the objective lens 110 is moved by an output from the adder circuit 208.
In the case when a portion for driving the objective lens 110 is of a sliding type (its elastic modulas is negligible), a force needed to start the motion of the objective lens 110 (i.e., this force is a drag due to its static friction) is large, as compared with a force needed to continue the motion of the objective lens 110 (i.e., this force is nearly a drag against its kinetic friction). In this case, if the objective lens 110 was moved solely by the TW circuit 206, the motion of the lens 110 would be irregular. Therefore, normally, the objective lens 110 is moved while always being reciprocated by a minute amount, using a voltage that has a shape as shown in FIG. 4A. This shape is produced by overlapping an output of the SW circuit 207 upon the triangle wave output of the TW circuit 206. Thus, the static friction is diminished.
In the above-discussed apparatus, when the objective lens 110 is moved and the focal point of the objective lens 110 is nearly brought onto the surface of the optical card 101, a voltage at the point A varies in a form of a letter S (a so-called S letter curve) as shown in FIG. 4B. Herein, in order to draw in or close the servo, the focusing controller 205 detects the fact that the voltage at the point A comes to zero (0) V at a time of t.sub.5. As a result, the focusing controller 205 supplies the signal D to the analog switch 203 to close the A point side and open the C point side. Thus, the focusing servo is drawn in.
FIG. 5 is a schematic view showing the structure of the tracking control circuit 117 shown in FIG. 1.
In FIG. 5, reference numeral 211 designates an amplifier for amplifying an electric tracking signal from the photoelectric conversion element 115 to a proper voltage. Reference numeral 213 designates an analog switch into one input terminal of which an output of the amplifier 211 is input through a point E and into the other input terminal of which an output of a triangle wave generating circuit or TW circuit 216 is input through a point F. One of the input terminals of the analog switch 213 is selected by a signal from the tracking controller 215. Reference numeral 214 designates a driver which causes a driving signal current to flow into the tracking coil 111 in response to a signal from the analog switch 213. Reference numeral 215 designates a tracking controller for controlling the entire tracking control circuit 117 in response to a signal 120 from the system controller 119. In FIG. 5, only a signal input from the tracking controller 215 into the analog switch 213 is indicated, but other signals (not shown) are also output from the tracking controller 215.
FIGS. 6A and 6B are respectively graphs illustrating changes in voltages at points F and E of the tracking control circuit 117, shown in FIG. 5.
The draw-in of the tracking servo will be described with reference to FIGS. 5, 6A and 6B.
Initially, as shown in FIG. 5, the E point side of the analog switch 213 is brought into an open state and the F point side thereof is brought into a closed state in response to a signal G from the tracking controller 215. Hence, the objective lens 110 is moved by an output from the TW circuit 216.
In the above-discussed apparatus, when the objective lens 110 is moved and the light spot intersects the track of the optical card 101, a signal E varies in a form of a letter S (a so-called S letter curve) as shown in FIG. 6B. Herein, the light spot is located on the track at a time of t.sub.0 at which the signal E initially becomes zero after this signal has passed a voltage of +V.sub.th. Therefore, the tracking servo can be drawn in by the tracking controller 215 detecting such a fact and then supplying the signal G to the analog switch 213 to close the E point side and open the F point side thereof.
The above-described prior art apparatus, however, has the following drawbacks:
First, in the draw-in of the focusing servo, if vibrations are imparted from outside at the time of the draw-in, the objective lens 110 is vibrated and the relative speed between the objective lens 110 and the optical card 101 becomes great at t.sub.5. Therefore, even if the servo is closed, the light spot deviates from an in-focus state.
Second, in,the draw-in of the tracking servo, if vibrations are imparted from outside at the time of the draw-in, the objective lens 110 is swayed relatively to the optical card 101. Further, after the signal E has passed +V.sub.th, the light spot is reversely moved due to the vibrations, as shown by an arrow in FIG. 7, and the signal E becomes zero at a position X.sub.1 where the light spot is derailed from the track. Therefore, the servo is closed at this point, and as a result, AT cannot be drawn in at a regular draw-in position.